The coating of electrically conductive substrates by electrodeposition is a well known and important industrial process. (For instance, electrodeposition is widely used in the automotive industry to apply primers to automotive substrates). In this process, a conductive article is immersed as one electrode in a coating composition made from an aqueous emulsion of film-forming polymer. An electric current is passed between the article and a counter-electrode in electrical contact with the aqueous emulsion, until a desired coating is produced on the article. The article to be coated is the cathode in the electrical circuit with the counter-electrode being the anode.
Resin compositions used in cathodic electrodeposition baths are also well known in the art. These resins are typically manufactured from polyepoxide resins which have been chain extended and adducted to include a nitrogen. The nitrogen is typically introduced through reaction with an amine compound. Typically these resins are blended with a crosslinking agent and then neutralized with an acid to form a water emulsion which is usually referred to as a principal emulsion.
The principal emulsion is combined with a pigment paste, coalescent solvents, water, and other additives (usually at the coating site) to form the electrodeposition bath. The electrodeposition bath is placed in an insulated tank containing the anode. The article to be coated is made the cathode and is passed through the tank containing the electrodeposition bath. The thickness of the coating is a function of the bath characteristics, the electrical operating characteristics, the immersion time, and so forth.
The coated object is removed from the bath after a set amount of time. The object is rinsed with deionized water and the coating is cured typically in an oven at sufficient temperature to produce crosslinking. It is typically covered with any of a variety of different topcoat systems (e.g. (basecoat/clearcoat.)
The prior art of cathodic electrodepositable resin compositions, coating baths, and cathodic electrodeposition processes are disclosed in U.S. Pat. Nos. 3,922,253; 4,419,467; 4,137,140; and 4,468,307.
An important step in the production of the cathodic electrodepositable polymer is the introduction of the amine to the epoxy compound. This is needed in order to make the polymer water soluble through the use of an acid counter-ion. Typically the epoxy is reacted with primary and/or secondary amine. It is important to have a high pH and stable dispersion. Current commercial electrocoat systems typically use ketimenes to introduce the amine functionality to the epoxy resins. This well known process is described in U.S. Pat. No. 4,017,438 which is incorporated herein by reference. However, ketimene must be protected from moisture, and it is time consuming to prepare. There is a need for an alternate method (other than ketimene) for introducing the amine functionality to the epoxy resin.